Sintered joints provide an alternative to soldered joints. A typical method of forming a sintered joint involves placing a metal powder, often in the form of a powder compact, between two work pieces to be joined and then sintering the metal powder. The resulting atomic diffusion of the metal atoms forms a bond between the two work pieces.
Metal nanopowders have been used to form sintered joints in the electronics industry, and are considered to be useful alternatives to lead-free soldering. The differing behaviour between nanomaterials and the corresponding bulk material is thought to be due to nanomaterials having a higher surface-to-volume ratio.
Sintering powders containing silver nanoparticles are known. Sintered joints formed by atomic diffusion of silver nanoparticles can be processed at a temperature significantly lower than the melting temperature of the bulk and can also be used for high temperature applications. The potential advantages, such as high temperature stability, high electrical and thermal conductivity, and good mechanical properties, make such sintering powders promising candidates for die attachment applications. However, the sintering temperatures of such sintering powders are still too high for effective use in most electronics applications.
Sintering temperatures may be reduced by applying an external pressure during sintering. Pressure-assisted low-temperature sintering of silver paste has been shown to be a viable alternative to solder reflow as a die-attachment method. The application of high pressure has been shown to significantly lower the sintering temperature, and the desired properties for die attachment can be achieved at a relatively faster rate resulting in the formation of a sintered joint within a few minutes. However, a large external pressure makes automation of the process difficult. Furthermore, application of a large external pressure may result in damage to the work pieces.
It is known to dispense solder paste for a variety of applications, but mostly as an alternative when wave solder or screen printing is not possible. Solder paste can be dispensed on a variety of surface mount applications on printed circuit boards, integrated circuit packages, and electrical component connectors. Typical problems of solder paste include: dripping, skipped dots, and inconsistent dispensing. Soft and hard solders are typically used in the electronic industries for die attached and dispensing. The soft solders are susceptible to fatigue failure under thermal cycling conditions. On the other hand, hard solders and glass matrix composites are used to enable devices to run at higher junction temperatures, but their higher elastic moduli and processing temperatures can generate high mechanical stresses in devices, and these materials also have relatively low thermal and electrical conductivities.